Processes for oxidative dehyrogenation

ABSTRACT

Processes for oxidative dehydrogenation of alkane to one or more olefins, exemplified by ethane to ethylene, are disclosed using novel catalysts. The catalysts comprise a mixture of metal oxides having as an important component nickel oxide (NiO), which give high conversion and selectivity in the process. For example, the catalyst can be used to make ethylene by contacting it with a gas mixture containing ethane and oxygen. The gas mixture may optionally contain ethylene, an inert diluent such as nitrogen, or both ethylene and an inert diluent.

This application is a continuation of U.S. application Ser. No.09/255,371, filed Feb. 22, 1999, now U.S. Pat. No. 6,355,854.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

This invention relates to methods and materials for the dehydrogenationof alkanes, particularly the conversion of ethane to ethylene, and moreparticularly, to mixed oxide catalysts for oxidative dehydrogenation ofethane.

DISCUSSION

Ethylene can be produced by thermal cracking of hydrocarbons, and bynonoxidative dehydrogenation or oxidative dehydrogenation of ethane(ODHE). The latter process is attractive for many reasons. For example,compared to thermal cracking, high ethane conversion can be achieved atrelatively low temperatures (about 400° C. or below). Unlike thermalcracking, catalytic ODHE is exothermic, requiring no additional heat tosustain reaction. Furthermore, in contrast to catalytic dehydrogenation,catalyst deactivation by coke formation should be minimal in ODHEbecause of the presence of oxygen in the reactor feed. Other alkanes cansimilarly be oxidatively dehydrogenated.

In the late seventies, Thorsteinson and coworkers first disclosed usefullow temperature ODHE catalysts comprised of mixed oxides containingmolybdenum, vanadium, and a third transition metal. E. M Thorsteinson etal., “The Oxidative Dehydrogenation of Ethane over Catalyst ContainingMixed oxide of Molybdenum and Vanadium,” 52 J. Catalysis 116-32 (1978).Later studies examined families of alumina-supported vanadium-containingoxide catalysts, MV and MVSb, where M is Ni, Co, Bi, and Sn. R. JuarezLopez et al., “Oxidative Dehydrogenation of Ethane on SupportedVanadium-Containing Oxides,” 124 Applied Catalysis A: General 281-96(1995). More recently, Schuurman and coworkers describe unsupportediron, cobalt and nickel oxide catalysts that are active in ODHE. Y.Schuurman et al., “Low Temperature Oxidative Dehydrogenation of Ethaneover Catalysts Based on Group VIII Metals,” 163 Applied Catalysis A:General 227-35 (1997). Although the mixed oxide catalysts reported byThorsteinson, Schuurman and others might be useful discoveries, theyrepresent a small fraction of potentially active inorganic oxidemixtures.

Industrial interest has stimulated investigations into new catalysts andmethods for improved performance (e.g., conversion and selectivity) forthe oxidative dehydrogenation of alkanes. There is a need for newdehydrogenation catalysts and methods.

SUMMARY OF THE INVENTION

This invention discloses catalysts and methods for the oxidativedehydrogenation of alkanes that have from 2 to 4 carbon atoms andparticularly ethane to ethylene. These catalysts primarily includenickel oxide and catalyze oxidative dehydrogenation with conversions ofgreater than 5% and with selectivity of greater than 70%. An object ofthe present invention is to provide a process whereby a C₂-C₄ alkane canbe oxidatively dehydrogenated to one or more olefins with relativelyhigh levels of conversion and selectivity. A further object of thisinvention is to provide a catalyst that selectively catalyzes thereaction of a C₂-C₄ alkane with oxygen to produce one or morecorresponding C₂-C₄ olefins with relatively high levels of conversionand selectivity, meaning preferably without the concurrent production ofsignificant amounts of by-products, such as carbon monoxide or carbondioxide.

In general, the catalysts of this invention have as a required componentnickel oxide and it is an object of this invention to provide a catalystfor the oxidative dehydrogenation of an alkane into one or more olefinshaving nickel oxide (NiO). The nickel oxide is combined with other metaloxides, dopants, carriers, binders and/or fillers into a catalyst thatis contacted with a gas mixture. The gas mixture comprises at least thealkane and oxygen, but may also include diluents (such as argon,nitrogen, etc.) or other components (such as water or carbon dioxide).Optionally, the gas mixture that contacts the catalyst may also includeone or more of the olefin products for an oxidative dehydrogenationprocess that converts a gas mixture having one ratio of alkane to alkeneto a gas mixture having a different ratio of alkane to alkene. Thecatalysts of this invention include a material or composition of matterhaving the empirical formula:Ni_(x)A_(j)B_(k)C_(l)O_(i)  I

-   -   wherein Ni is nickel and x is in the range of about 0.1-0.96;    -   A is selected from the group consisting of Nb, Ta, Co and        combinations thereof and j is in the range of from about 0-0.8;    -   B is an element selected from the group consisting of alkali        metals, alkaline earths, or lanthanides and combinations        thereof, including Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Mn, La,        Ce, Pr, Nd, Sm and combinations thereof and k is in the range of        from 0-0.5;    -   C is an element selected from the group consisting of Sn, Al,        Fe, Si, B, Sb, Tl, In, Ge, Cr, Pb and combinations thereof and l        is in the range of from 0-0.5;    -   i is a number that satisfies the valence requirements of the        other elements present; and    -   the sum of j, k and l is at least 0:04.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows ethane conversion and ethylene selectivity as a function ofreaction temperature for Ni—Nb oxide mixtures and for an optimizedMo—V—Nb catalyst.

FIG. 2 shows ethane conversion and ethylene selectivity as a function ofoxygen content of reactor feed for Ni—Nb oxide mixtures and for anoptimized Mo—V—Nb catalyst.

FIG. 3 shows ethane conversion and ethylene selectivity as a function ofoxygen content of reactor feed for Ni—Co—Nb oxide mixtures and for anoptimized Mo—V—Nb catalyst.

DETAILED DESCRIPTION

The present invention includes nickel oxide catalysts for oxidativedehydrogenation of alkanes having 2, 3 or 4 carbon atoms to thecorresponding olefin(s). The invention is exemplified for ethane toethylene. An important feature of this invention is the relatively highpercentages of conversion and selectivity that the catalyst provides fora dehydrogenation process. As used herein the phrase selectivity (alsoknown as efficiency) refers to a percentage that reflects the amount ofdesired olefin product produced as compared to the total carbon productsas follows:${\%\quad{selectivity}} = {100 \times \frac{{Moles}\quad{of}\quad{alkene}\quad{produced}}{\text{The molar alkene-equivalent sum (carbon basis) ofall carbon-containing~~~products, excluding the alkanein the effluent.}}}$

Similarly as used herein the term conversion refers to a percentage thatreflects the amount of alkane provided to the reaction as compared tothe total carbon products as follows: $\begin{matrix}{{\%\quad{conversion}} = {100 \times \frac{\text{The molar alkane-equivalent sum (carbon~~basis) ofall carbon-containing~~~products, excluding the alkanein the effluent.~~~~}}{\text{Moles of alkane in the reaction mixture, whichis fed to the catalyst in the reactor}}}} & \quad\end{matrix}$

These expressions are the theoretical expressions for selectivity andconversion. Simplified formulas have been used in the examples herein,and may be used by those of skill in the art. The simplified formula for% selectivity is % selectivity=100×[(moles of alkene)/(moles ofalkene+((moles of carbon dioxide)/2))]. Similarly the simplified formulafor % conversion is % conversion=100×[(moles of alkene+((moles of carbondioxide)/2))/(moles of alkane)]. Although these simplified formulas areused, typically the only products observed in the ethane to ethyleneoxidative dehydrogenation reaction (using an ethane and oxygen gas feed)are ethylene and carbon dioxide. In these formulas, those of skill inthe art will recognize that an alkene is an olefin. These calculationsare straightforward when ethane and propane are the alkanes. When butaneis the alkane, the possibility exists that the product is one or more of1-butene, 2-butenes or 1,3-butadiene. Thus, the percentages forselectivity and conversion are percentages of one or more of thesedehydrogenated products of butane. Using the catalysts and process thatare disclosed herein, selectivity of dehydrogenation of alkane to thecorresponding olefin can be greater than 70%, 75%, 80%, 85% and mostpreferably greater than 90%. Also, the conversion can be greater than 5%and preferably greater than 10% or greater than 15%. In fact, theconversions may be 20% or greater. Surprisingly, the experimentalresults suggest that the selectivity does not alter significantly withthe conversion, meaning that within experimental error the selectivityis more or less independent of the conversion.

The catalysts of this invention include a composition of matter ormaterial having the empirical formula:Ni_(x)A_(j)B_(k)C_(l)O_(i)  I

-   -   wherein Ni is nickel and x is in the range of about 0.1-0.96;    -   A is selected from the group consisting of Nb, Ta, Co and        combinations thereof and j is in the range of from about 0-0.8;    -   B is an element selected from the group consisting of alkali        metals, alkaline earths, or lanthanides and combinations        thereof, including Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Mn, La,        Ce, Pr, Nd, Sm and combinations thereof and k is in the range of        from 0-0.5;    -   C is an element selected from the group consisting of Sn, Al,        Fe, Si, B, Sb, Tl, In, Ge, Cr, Pb and combinations thereof and l        is in the range of from 0-0.5    -   i is a number that satisfies the valence requirements of the        other elements present; and    -   the sum of j, k and l is at least 0.04.        Catalysts defined by this formula include nickel that is        substantially in the oxidized state; meaning that there may be        nickel metal present, but it will not be the majority. Nickel        oxide (NiO) is present in an amount preferably of at least 20%        by weight, more preferably at least 50% by weight and most        preferable at least 60% by weight. In some preferred        embodiments, Nb and Ta are included together in the composition        (with Co being optional) and j may range from about 0.05-0.8.        Generally, x may range from about 0.1-0.96 (e.g., 10-96%),        preferably from about 0.3 to about 0.85, more preferably from        about 0.5 to about 0.8 and most preferably from about 0.6 to        about 0.8. Generally, j may range from about 0 to about 0.8        (e.g., 0-80%), but preferably ranges from 0.04 to about 0.5,        more preferably from about 0.04 to 0.4 and alternatively from        about 0.3 to about 0.4. Generally, k and l each may range from        about 0 to about 0.5 (e.g., 0-50%), but preferably ranges from 0        to about 0.4, more preferably from about 0 to 0.1 and most        preferably from about 0 to about 0.05. Within these ranges, the        sum of j, k and l will be at least about 0.04 but may range as        high as about 0.9. In other embodiments, the sum of j, k and l        will be no more than 0.5, 0.4 and optionally 0.3. In some        embodiments, Nb and Ta are included together in the composition        (with Co being optional) and j may range from about 0.04 to        about 0.8 or in any of the other listed ranges for j.

In still other embodiments, the catalysts can be represented by theempirical formula:Ni_(a)Co_(b)Nb_(c)Ta_(d)Sn_(e)K_(f)Al_(g)Fe_(h)O_(i).  IIIn formula II, subscripts b, c and d are numbers greater than or equalto zero but less than one. At least one of b, c and d is nonzero.Subscripts e and f are numbers greater than or equal to zero but lessthan or equal to about 0.35; subscripts g and h are numbers greater thanor equal to zero but less than or equal to about 0.10; and subscript ais a number greater than zero but less than one, and satisfies theexpression:a≦1−b−c−d−e−f−g−h.  IIIIn equation II, subscript i is a number that satisfies valencerequirements of elements listed in the formula.

The catalyst is supplied to the reactor as a fixed bed—the catalyst mayor may not be supported on a carrier. If a carrier is used, the carriermay be selected from the group consisting of alumina, silica, titania,zirconia, magnesia, zeolites, clays or mixtures thereof. The catalystmay take any form, including powder, split, granular, pellets or ashaped catalyst, such as tablets, rings, cylinders, stars, rippedbodies, extrudates, etc. known to those of skill in the art. Forexample, the shaping of the mixture of starting composition may becarried out by compaction (for example tableting or extrusion) with orwithout a prior kneading step, if necessary with addition ofconventional auxiliaries, for example graphite or stearic acid or itssalts as lubricants. In the case of unsupported catalysts, thecompaction gives the desired catalyst geometry directly. Hollowcylinders may have an external diameter and length of from 2 to 10 mmand a wall thickness of from 1 to 3 mm. Very generally, the mixture ofstarting composition metal may be shaped either before or after thecalcination. This can also be carried out, for example, by comminutingthe mixture after the calcination and applying it to inert supports toproduce coated catalysts. However, the application can also be carriedout before the final calcination. The catalyst may be diluted (e.g.,have its density reduced) with binders and/or inert fillers, which areknown to those of skill in the art, including for example quartz chips,sand or cement. Diluents may be added to the catalyst in the range offrom about 0 to about 30% by volume, preferably in the range of fromabout 10 to about 25% by volume. Preferred diluents improve the heatremoval or heat transfer of the catalyst to help avoid hot spots or tomodify hot spots. Binders generally provide mechanical strength to thecatalyst and may be added in the range of from about 0-30% by volume,preferably in the range of from about 5 to about 25% by volume. Usefulbinders include silica sol, silica, alumina, diamateous earth, hydratedzirconia, silica aluminas, alumina phosphates, naturally occurringmaterials and cement and combinations thereof. See, e.g., the discussionof supports, shapes, binders and fillers in U.S. Pat. Nos. 5,376,613,5,780,700 and 4,250,346, each of which is incorporated herein byreference for all purposes. The percentages or amounts of binders,fillers or organics referred to herein relate to the startingingredients prior to calcination. Thus, the above is not intended toimply statements on the actual bonding ratios, to which the invention isnot restricted; for example during calcination other phases can form.

The disclosed mixed oxides can be used to make an olefin from therespective alkane, for example, ethylene from ethane, by contactingthem, in a pressure vessel or reactor, with a gas mixture comprised ofthe alkane and oxygen. Contact between the catalyst and the gas mixtureoccurs by passing the gas mixture through the interstices in the fixedbed, which ensures intimate contact between the gas mixture and thecatalyst. Also, the gas mixture may be passed over the catalyst surface,in situations were gas cannot pass through the catalyst. During contact,the catalyst and the gas mixture are maintained at a temperature betweenabout 250° C. and 400° C., thus the reaction temperature is typically400° C. or less, preferably 325° C. or less and alternatively 300° C. orless. The reaction pressure during contacting can range from about 0.5to 20 bar and for a time of between 100 milliseconds to about 10seconds. Generally, the gas mixture that contacts the catalyst comprisesthe alkane to be dehydrogenated and oxygen or an oxygen source in thereactor. The gas mixture may also include diluents such as nitrogen,argon or carbon dioxide. In other embodiments, the gas mixture may alsoinclude water (e.g., steam) or butylenes or ethylene or propylene.

The disclosed catalyst can convert alkane to olefin (e.g., ethane toethylene) even in the presence of significant amounts of olefin (e.g.,ethylene) in the reactor feed. Typically the gas mixture that iscontacted with the catalyst has an oxygen content in the range of fromabout 0.01 to about 50% by volume and the alkane in the range of fromabout 5-99.99% by volume. A preferred range includes 0.01 to 20% byvolume of oxygen and 10 to 90% by volume of alkane (e.g., ethane,propane or butane). In an alternative embodiment, the gas mixture canfurther include the olefin of the corresponding alkane that is beingdehydrogenated. For example, an ethane gas feed may also containethylene, such that the catalyst and methods of this invention willconvert such a gas stream to a more olefin rich content. For example, a70%/30% by volume ethane/ethylene reactant gas can be converted to a60%/40% by volume ethane/ethylene product or a 50%/50% by volumeethane/ethylene product. Generally, mixed gas reactant streams may havean alkane/olefin range from about 99%/1% by volume to about 50%/50% byvolume. In another alternative, the gas mixture that contacts thecatalyst may contain raffinate II, which is a mixture of butane,2-butenes and 1-butene. Because of the ability of these catalysts toperform the desired dehydrogenation selectively, mixed streams may beconverted into more uniform streams.

Generally, the catalyst can be prepared by sol-gel, freeze drying, spraydrying, precipitation, impregnation, incipient wetness, sprayimpregnation, ion exchange, wet mix/evaporation, dry mix/compacting,high coating, fluid bed coating, bead coating, spin coating, physicalvapor deposition (sputtering, electron beam evaporation, laser ablation)and chemical vapor deposition. Thus, any technical or non-technicaltechnique may be used. Also the catalyst may take any of the formsdiscussed above (granular, tablets, etc.).

One method for making the catalysts of this invention is by mixingsolutions or suspensions that include the metal precursors, driving offthe solvent and converting at least part of the precursors into oxides.See also U.S. Pat. No. 4,250,346, incorporated herein by reference. Themetal precursors comprise the desired metal in a solution or suspensionin a desired amount in a suitable solvent. The metal precursor solutionis prepared by dissolving a least part of a soluble compound of each ofthe metals or elements so as to provide the desired ratios of the metalsor elements in the catalyst composition. One specific preferred metalprecursor is a Ta precursor that is prepared by slowly hydrolyzingtantalum ethoxide in oxalic acid and water and then diluting making atantalum oxalate. This process works particularly well for group 5metals, such as Ta and Nb and is preferred because it provides a solubleTa or Nb precursor, it is chloride free and generally provides betterperformance. Previous Ta solutions included chloride, which is notdesirable generally. Details of specific metal precursors are disclosedin the examples. A metal precursor solution or suspension may beprepared for each metal or element in the desired catalyst composition,or a single metal precursor solution may include multiple metals orelements. After mixing the metal precursors, the solvent is driven offby any one a variety of techniques known to those of skill in the art,such as evaporation, freeze drying, etc. Thereafter, the composition iscalcinated. Calcination is typically carried out at a temperature in therange of from about 200° C. to about 1000° C. Preferred calcinationtemperatures are less than 600° C. or less than 500° C. and greater than250° C. or greater than 300° C. Calcination of the samples can be for{fraction (1/2)} hour to 24 hours, more specifically from 1 to 12 hoursand even more specifically from about 1 to 6 hours. Calcination may becarried out in an atmosphere of air. Preferably, there is a ramp up inthe calcination temperature, as disclosed in the examples.

Choice of calcination conditions can affect the activity of the catalystdepending on the catalyst composition and dehydrogenation reactionconditions. For example, by lowering the calcination temperature,Ni—Nb—Ta oxides are generally more active for catalyzing ethaneoxidative dehydrogenation at low temperature with higher conversions. Asspecifically shown in the examples, a calcination temperature forNi—Nb—Ta oxides of about 400° C. gave generally lower conversions incomparison to a calcination temperature of about 300° C.

One preferred method is an aqueous method where various aqueoussolutions comprised of water-soluble metal precursors are combined inproper volumetric ratios to obtain mixtures having desired metalcompositions. Next, water is separated from the mixtures bylyophilization or precipitation. Lyophilization refers to freezing theresulting mixture under liquid nitrogen, and then placing the mixture ina high vacuum so that the water (ice) sublimes, leaving behind mixturesof dry metal precursors. Precipitation refers to separating dissolvedmetal ions by adding one or more chemical reagents that will precipitatesparingly soluble salts of the metal ions. Such chemical reagents mayprovide ions that shift ionic equilibria to favor formation of insolublemetal salts (common ion effect), or may bind with metal ions to formuncharged, insoluble coordination compounds (complexation). In addition,such reagents may oxidize or reduce metal ions to form ionic speciesthat produce insoluble salts. Other precipitation mechanisms includehydrolysis, in which metal ions react with water in the presence of aweak base to form insoluble metal salts. Whatever the mechanism, theprecipitate is separated from the remaining solution by firstcentrifuging the solutions and then decanting the supernatant; residualwater can be removed by heating the precipitates or in vacuum. Finally,whether prepared by the sol-gel method or by the aqueous methods, thedry mixtures are calcined and may be ground to ensure a consistent bulkdensity among samples.

In addition, the usefulness of the catalysts of this invention is notnecessarily limited to dehydrogenation reactions. Other useful reactionsthat may be performed with the catalysts include selective oxidation,ammoxidation, amination, homo and cross carbon-carbon coupling,dimerization and isomerization reactions.

EXAMPLES

The following examples are intended as illustrative and non-limiting,and represent specific embodiments of the present invention.

Example 1 Ni—Co—Nb Oxide Mixtures

Catalysts were prepared by an aqueous method. One molar nickel and 1.0 Mcobalt stock solutions were prepared by dissolving 29.088 g of nickel(II) nitrate hexahydrate in distilled water to a final volume of 100 mland by dissolving 29.129 g of cobalt (II) nitrate hexahydrate indistilled water to a final volume of 100 ml, respectively. A 1.0 Mniobium stock solution was prepared by slowly hydrolyzing 100 mmolniobium ethoxide in an oxalic acid solution (2.7 M) in distilled waterat 60° C. and diluted to 100 ml in volume after cooling to 25° C. ACAVRO automated liquid dispensing system was used to deliver aliquots ofthe aqueous stock solutions into 28 vessels. Each vessel contained 2250μl of solution, and the molar concentrations of the metal ions in eachvessel were given by expressions: $\begin{matrix}{{\lbrack{Ni}\rbrack_{i,j} = \frac{2000 - {300\left( {i - 1} \right)}}{2250}},M} & {IV} \\{{\lbrack{Co}\rbrack_{i,j} = \frac{200 + {300\left( {j - 1} \right)}}{2250}},M} & V \\{{\lbrack{Nb}\rbrack_{i,j} = \frac{50 + {75\left( {i - j} \right)}}{2250}},M} & {VI}\end{matrix}$In expressions IV through VI, subscripts i and j represent row andcolumn indices of a 7-by-7 triangular array, respectively, and i≧j, i=1,. . . , 7, and j=1, . . . , 7.

Water was separated from the mixtures by lyophilization (freeze drying).Each of the 28 aqueous solutions were frozen under liquid nitrogen, andthen placed in a high vacuum to vaporize the ice. The resulting drymixtures were placed in an oven for calcination. The temperature of theoven was increased from room temperature to 120° C. at a rate of 1°C./min. The oven temperature was maintained at 120° C. for 2 hours, andwas then ramped at 1° C./min. to 180° C. The oven temperature was heldat 180° C. for 2 hours and was then ramped at 2° C./min. to 400° C.After 8 hours at 400° C., the oxide mixtures were removed from the ovenand were allowed to cool to room temperature. The bulk samples wereground with a spatula to ensure consistent bulk density.

The catalyst compositions were each contacted with a gas mixturecomprised of ethane and oxygen and by measuring the composition of thegas mixture following contact with the bulk samples. The best performingcatalysts were those that yielded the highest ethane conversion andethylene selectivity. Contacting was carried out in a 48-vessel parallelfixed bed reactor as described in U.S. patent application Ser. No.09/093,870, “Parallel Fixed Bed Reactor and Fluid Contacting Apparatusand Method,” filed Jun. 9, 1998, which is incorporated herein byreference.

Table 1 lists the composition and mass of Ni—Co—Nb oxide mixturestested. High purity ethane and 14.4% O₂ in N₂ were obtained fromMATHESON. Pure N₂ was obtained from an in-house supply line. Afterloading the reactor vessels with the 28 catalysts, the vessels werepurged with N₂ to remove residual O₂. Next, the vessels were purged withethane for another ten minutes. The composition of the effluent fromeach of the vessels was measured by gas chromatography (GC) to ensurethat the ethane level had reached 95% prior to screening. The O₂/N₂mixture was then added so that the reactant flow rate was 0.524 sccm perminute per reactor vessel, and the reactant gas composition was 40.1%C₂H₆, 8.4% O₂ and 51.5% N₂. Gas flow stability was measured periodicallyby GC. Two VARIAN 3800, 3-channel gas chromatographs were used to detectethylene in vessel effluent. Each of the three channels contained 6-inchHAYESEP columns, methanizers, and flame-ionization detectors. CO, CO₂,C₂H₄, and C₂H₆ were separated to baseline in about three minutes. Theresponses of the flame ionization detectors and the methanizers werecalibrated using a standard gas mixture containing 2.0% CO, 2.0% CO₂,6.0% C₂H₄, 30.0% C₂H₆, 4.0% O₂ and the balance N₂. Five calibrationexperiments were carried out to generate calibration coefficients.Reactor (vessel) temperature was maintained at 300° C., and reactionswere carried out at 15 psia. Tables 2 and 3 list ethane conversion andethylene selectivity, respectively, for each of the Ni—Co—Nb oxidemixtures listed in Table 1.

Example 2 Ni—Co—Nb Oxide Mixtures

Table 4 lists composition and mass of Ni—Co—Nb oxides belonging to asecond library. Like the bulk samples described in Example 1, the oxidemixtures shown in Table 4 were prepared from aqueous stock solutions ofnickel (II) nitrate hexahydrate, cobalt (II) nitrate hexahydrate andniobium (V) oxalate. A CAVRO automated liquid dispensing system was usedto deliver aliquots of the aqueous stock solutions into vessels. Waterwas separated from the mixtures by lyophilization, and the resulting drymixtures were placed in an oven to oxidize the metal precursors inaccordance with the temperature-time profile described in Example 1. Thebulk samples were ground with a spatula to ensure consistent bulkdensity, and were evaluated for catalytic performance by contacting eachsample with ethane and oxygen in a parallel fixed bed reactor. Reactionconditions were the same as those used to evaluate the mixed oxidesshown in Table 1 of Example 1. Table 5 and 6 list ethane conversion andethylene selectivity at 300° C., respectively, for each of the Ni—Co—Nboxide mixtures listed in Table 4.

Example 3 Ni—Co—Nb Oxide Mixtures

Table 7 lists composition and mass of Ni—Co—Nb oxides belonging to athird library. Like the bulk samples described in Example 1, the oxidemixtures shown in Table 7 were prepared from aqueous stock solutions ofnickel (II) nitrate hexahydrate, cobalt (II) nitrate hexahydrate andniobium (V) oxalate. A CAVRO automated liquid dispensing system was usedto deliver aliquots of the aqueous stock solutions into vessels. Waterwas separated from the mixtures by lyophilization, and the resulting drymixtures were placed in an oven to oxidize the metal precursors inaccordance with the temperature-time profile described in Example 1. Thebulk samples were ground with a spatula to ensure consistent bulkdensity, and were evaluated for catalytic performance in ODHE bycontacting each sample with ethane and oxygen in a parallel fixed bedreactor. Reaction conditions were the same as those used to evaluate themixed oxides shown in Table 1 of Example 1, except that the reactantflow rate was 1.048 sccm per minute per vessel. Table 8 and 9 listethane conversion and ethylene selectivity at 300° C., respectively, foreach of the Ni—Co—Nb oxide mixtures listed in Table 7.

Example 4 Ni—Co—Nb Oxide Mixtures

66 bulk samples of Ni—Co—Nb oxide mixtures were prepared and tested. Thecompositions of the oxide mixtures, which are listed in Table 10,encompassed a full range of ternary mixtures. Like the bulk samplesdescribed in Example 1, the oxide mixtures shown in Table 10 wereprepared from aqueous stock solutions of nickel (II) nitratehexahydrate, cobalt (II) nitrate hexahydrate and niobium (V) oxalate. ACAVRO automated liquid dispensing system was used to deliver aliquots ofthe aqueous stock solutions into vessels. The samples were lyophilized,calcined and ground in a manner similar to the mixed oxides shown inTable 1 of Example 1, and were evaluated for catalytic performance bycontacting each sample with ethane and oxygen in a parallel fixed bedreactor. Reaction conditions were the same as those used to evaluate themixed oxides shown in Table 7 of Example 3. Tables 11 and 12 list ethaneconversion and ethylene selectivity at 300° C., respectively, for eachof the Ni—Co—Nb oxide mixtures listed in Table 12.

Example 5 Ni—Co—Nb Oxide Mixtures

Table 13 lists composition and mass of Ni—Co—Nb oxides belonging to afourth library. Like the bulk samples described in Example 1, the oxidemixtures shown in Table 13 were prepared from 1.0 M nickel (II) nitratehexahydrate, 1.0 M cobalt (II) nitrate hexahydrate and 1.0 M niobium (V)oxalate aqueous stock solutions. A CAVRO automated liquid dispensingsystem was used to deliver aliquots of the aqueous stock solutions intovessels. Each vessel contained about 1.9 ml of solution. In contrast toExample 1, the metal precursors were separated from the aqueous phase byprecipitation. One ml of ammonium hydroxide (28% ammonia in water) wasadded to each of the solutions resulting in a solid precipitate. Thesolid precipitate was separated from the aqueous phase by centrifugingat 4000 rpm for 20 minutes, followed by decanting the supernatant. Thesolid was dried in a vacuum oven at 60° C. for about an hour, and thencalcined in accordance with the temperature-time profile described inExample 1. The bulk samples were ground with a spatula to ensureconsistent bulk density, and were evaluated for catalytic performance inODHE by contacting each sample with ethane and oxygen in a parallelfixed bed reactor. Reaction conditions were the same as those used toevaluate the mixed oxides shown in Table 7 of Example 3. Table 14 and 15list ethane conversion and ethylene selectivity at 300° C.,respectively, for each of the Ni—Co—Nb oxide mixtures listed in Table13.

Example 6 Ni—Nb and Ni—Co—Nb Oxide Mixtures: Effect of Sample Mass,Reaction Temperature and Oxygen Content of Reactor Feed on EthaneConversion and Selectivity; Comparison with Optimized Mo—V—Nb OxideCatalyst

FIG. 1 illustrates ethane conversion and ethylene selectivity as afunction of reaction temperature for two of the catalysts in Table 13 ofExample 5—Ni_(0.63)Nb_(0.37) and Ni_(0.55)Nb_(0.45)—as well as anoptimized Mo—V—Nb catalyst. The catalysts were evaluated in a parallelfixed bed reactor at temperatures ranging from 250° C. to 350° C. TheNi—Nb catalysts were tested at two different sample masses, while theMo—V—Nb catalyst was tested at three different sample masses. Reactantflow rate was 1.048 sccm per minute per reactor vessel (sample), and thereactant gas was comprised of 40.1% C₂H₆, 8.4% O₂ and 51.5% N₂. Ethaneconversion curves are shown for Ni_(0.63)Nb_(0.37) (10.0 mg, 37.0 mg)202, 204; Ni_(0.55)Nb_(0.45) (16.4 mg, 48.9 mg) 206, 208; and Mo—V—Nb(12.3 mg, 23.4 mg, 72.2 mg) 210, 212, 214. Ethylene selectivity curvesare shown for Ni_(0.63)Nb_(0.37) (10.0 mg, 37.0 mg) 216, 218;Ni_(0.55)Nb_(0.45) (16.4 mg, 48.9 mg) 220, 222; and Mo—V—Nb (12.3 mg,23.4 mg, 72.2 mg) 224, 226, 228.

FIG. 2 illustrates ethane conversion and ethylene selectivity as afunction of oxygen content of the reactor feed for the two Ni—Nbcatalysts and the optimized Mo—V—Nb catalyst. The catalysts wereevaluated in the parallel fixed bed reactor at 300° C. As in FIG. 2, theNi—Nb catalysts were tested at two different sample masses, and theMo—V—Nb catalyst was tested at three different sample masses. In allcases, reactant flow rate was 1.048 sccm per minute per reactor vessel(sample). The reactant feed was comprised of 0% to 21% O₂, 51.5% N₂, andthe balance C₂H₆. Ethane conversion curves are shown forNi_(0.63)Nb_(0.37) (10.0 mg, 37.0 mg) 302, 304; Ni_(0.55)Nb_(0.45) (16.4mg, 48.9 mg) 306, 308; and Mo—V—Nb (12.3 mg, 23.4 mg, 72.2 mg) 310, 312,314. Ethylene selectivity curves are shown for Ni_(0.63)Nb_(0.37) (10.0mg, 37.0 mg) 316, 318; Ni_(0.55)Nb_(0.45) (16.4 mg, 48.9 mg) 320, 322;and Mo—V—Nb (12.3 mg, 23.4 mg, 72.2 mg) 324, 326, 328.

FIG. 3 illustrates ethane conversion and ethylene selectivity as afunction of the amount of oxygen in the reactor feed for four catalystsshown in Table 13 that contain small amounts of cobalt-Ni_(0.8)Co_(0.04)Nb_(0.16), Ni_(0.65)Co_(0.04)Nb_(0.31),Ni_(0.58)Co_(0.04)Nb_(0.39) and Ni_(0.60)Co_(0.08)Nb_(0.32). Forcomparison, FIG. 3 also shows ethane conversion and ethylene selectivityfor the optimized Mo—V—Nb catalyst. The catalysts were evaluated in theparallel fixed bed reactor at 300° C. The Ni—Co—Nb catalysts were eachtested at one sample mass, and the Mo—V—Nb catalyst was tested at threedifferent sample masses. In all cases, reactant flow rate was 1.048 sccmper minute per reactor vessel (sample). The reactant feed was comprisedof 0% to 21% O₂, 51.5% N₂, and the balance C₂H₆. Ethane conversioncurves are shown for Ni_(0.81)Co_(0.04)Nb_(0.16) (35.8 mg) 402;Ni_(0.65)Co_(0.04)Nb_(0.31) (32.4 mg) 404; Ni_(0.58)Co_(0.04)Nb_(0.39)(38.3 mg) 406; Ni_(0.60)Co_(0.08)Nb_(0.32) (30.2 mg) 408; and Mo—V—Nb(12.3 mg, 23.4 mg, 72.2 mg) 410, 412, 414. Ethylene selectivity curvesare shown for Ni_(0.81)Co_(0.04)Nb_(0.16) (35.8 mg) 416;Ni_(0.65)Co_(0.04)Nb_(0.31) (32.4 mg) 418; Ni_(0.58)Co_(0.04)Nb_(0.39)(38.3 mg) 420; Ni_(0.60)Co_(0.08)Nb_(0.32) (30.2 mg) 422; and Mo—V—Nb(12.3 mg, 23.4 mg, 72.2 mg) 424, 426, 428.

Example 7 Ni—Nb—Ta—K Oxide Mixtures

Table 16 lists composition and mass of a focused Ni—Nb—Ta—K oxidelibrary. The oxide mixtures were selected based on the primary screeningresults shown in Table 21 and were prepared from 1.0 M nickel (II)nitrate hexahydrate, 0.70 M niobium (V) oxalate, 0.87 M tantalum oxalateand 1.07 M potassium nitrate aqueous stock solutions. A CAVRO automatedliquid dispensing system was used to deliver aliquots of the aqueousstock solutions into vessels. Water was separated from the mixtures bylyophilization, and the resulting dry mixtures were placed in an oven tooxidize the metal precursors in accordance with the temperature-timeprofile described in Example 1. The bulk samples were ground with aspatula to ensure consistent bulk density, and were evaluated forcatalytic performance in ODHE by contacting each sample with ethane andoxygen in the parallel fixed bed reactor. Reactant flow rate was 1.048sccm per minute per reactor vessel (sample), and the reactant gas wascomprised of 40.1% C₂H₆, 8.4% O₂ and 51.5% N₂. Tables 17 and 18 listethane conversion and ethylene selectivity at 300° C., respectively, foreach of the Ni—Nb—Ta—K oxide mixtures listed in Table 16.

Example 8 Ni—Nb—Ta Oxide Mixtures

Table 19 lists composition and mass of a Ni—Nb—Ta oxide library. Bulksamples of the oxide mixtures shown in Table 19 were prepared from 1.0 Mnickel (II) nitrate hexahydrate, 1.0 M niobium (V) oxalate and 1.0 Mtantalum oxalate aqueous stock solutions. A CAVRO automated liquiddispensing system was used to deliver aliquots of the aqueous stocksolutions into vessels. Each vessel contained about 1.9 ml of solution.Like Example 5, the metal precursors were separated from the aqueousphase by precipitation. One ml of ammonium hydroxide (28% ammonia inwater) was added to each of the solutions resulting in a solidprecipitate. The solid precipitate was separated from the aqueous phaseby centrifuging at 4000 rpm for 20 minutes, followed by decanting thesupernatant. The solid was dried in a vacuum oven at 60° C. for about anhour, and then calcined in accordance with the temperature-time profiledescribed in Example 1. The bulk samples were ground with a spatula toensure consistent bulk density, and were evaluated for catalyticperformance in ODHE by contacting each sample with ethane and oxygen ina parallel fixed bed reactor. Reactant flow rate was 1.048 sccm perminute per reactor vessel (sample), and the reactant gas was comprisedof 40.1% C₂H₆, 8.4% O₂ and 51.5% N₂. Tables 20 and 21 list ethaneconversion and ethylene selectivity at 300° C., respectively, for eachof the Ni—Nb—Ta oxide mixtures listed in Table 19.

Example 9 Ni—Nb—Ta Oxide Mixtures: Ethylene in Reactor Feed

Table 22 lists composition and mass of a Ni—Nb—Ta oxide library. Theoxide mixtures shown in Table 22 were prepared from 1.0 M nickel (II)nitrate hexahydrate, 1.0 M niobium (V) oxalate and 1.0 M tantalumoxalate aqueous stock solutions, as disclosed above. A CAVRO automatedliquid dispensing system was used to deliver aliquots of the aqueousstock solutions into vessels. Each vessel contained about 3.3 ml ofsolution. The metal precursors were from the aqueous phase byprecipitation. About 2.9 ml of a 1.57 M ammonium carbonate solution wasadded to each of the solutions resulting in a solid precipitate. Thesolid precipitate was separated from the aqueous phase by centrifugingat 4000 rpm for 20 minutes, followed by decanting the supernatant. Thesolid was dried in a vacuum oven at 60° C. for about an hour, and thencalcined in accordance with the temperature-time profile described inExample 1. The bulk samples were ground with a spatula to ensureconsistent bulk density, and were evaluated for catalytic performance inODHE by contacting each sample with ethane and oxygen in a parallelfixed bed reactor. Reactant flow rate was 1.048 sccm per minute perreactor vessel (sample), and the reactant gas was comprised of 40.1%C₂H₆, 8.4% O₂ and 51.5% N₂. Table 23 and 24 list ethane conversion andethylene selectivity at 300° C., respectively, for each of the Ni—Nb—Taoxide mixtures listed in Table 22. Table 25 and 26 list ethaneconversion and ethylene selectivity at 325° C.

To determine the effect of ethylene in the reactor feed on ethaneconversion and ethylene selectivity, the mixed oxide samples listed inTable 22 were contacted with a gas mixture comprised of 11.2% C₂H₄,28.1% C₂H₆, 0.8% CO₂, 8.4% O₂ and 51.5% N₂. Reactant flow rate wasmaintained at 1.048 sccm per minute per reactor vessel (sample), and thefractions of C₂H₄, C₂H₆ and CO₂ in the reactor feed were verified duringscreening by measuring the composition of gas effluent from blankvessels in the parallel fixed bed reactor. Tables 27 and 28, which listchanges in ethane and ethylene concentration following contact with theNi—Nb—Ta oxide mixtures, show significant ethane conversion to ethyleneat 325° C. Table 29 lists CO and CO₂ production at 325° C.

Example 10 Ni—Nb—Ta Oxide Mixtures: Ethylene in Reactor Feed

Table 30 lists composition and mass of another Ni—Nb—Ta oxide library.The oxide mixtures shown in Table 30 were prepared from 1.0 M nickel(II) nitrate hexahydrate, 1.0 M niobium (V) oxalate and 1.0 M tantalumoxalate aqueous stock solutions. A CAVRO automated liquid dispensingsystem was used to deliver aliquots of the aqueous stock solutions intovessels. Each vessel contained about 3.3 ml of solution. The metalprecursors were separated from the aqueous-phase by precipitation. About2.9 ml of a 1.57 M ammonium carbonate solution was added to each of thesolutions resulting in a solid precipitate. The solid precipitate wasseparated from the aqueous phase by centrifuging at 4000 rpm for 20minutes, followed by decanting the supernatant. The solid was dried in avacuum oven at 60° C. for about an hour, and then calcined in accordancewith the temperature-time profile described in Example 1. The bulksamples were ground with a spatula to ensure consistent bulk density,and were evaluated for catalytic performance in ODHE by contacting eachsample with ethane and oxygen in a parallel fixed bed reactor. Reactantflow rate was 1.048 sccm per minute per reactor vessel (sample), and thereactant gas was comprised of 40.1% C₂H₆, 8.4% O₂ and 51.5% N₂. Table 31and 32 list ethane conversion and ethylene selectivity at 300° C.,respectively, for each of the Ni—Nb—Ta oxide mixtures listed in Table30. Table 33 and 34 list ethane conversion and ethylene selectivity at325° C.

To determine the effect of ethylene in the reactor feed on ethaneconversion and ethylene selectivity, the mixed oxide samples listed inTable 30 were contacted with a gas mixture comprised of 11.2% C₂H₄,28.5% C₂H₆, 8.4% O₂ and 51.5% N₂. Reactant flow rate was maintained at1.048 sccm per minute per reactor vessel (sample), and the fractions ofC₂H₄, C₂H₆ and CO₂ in the reactor feed were verified during screening bymeasuring the composition of gas effluent from blank vessels in theparallel fixed bed reactor. Tables 35 and 36, which list changes inethane and ethylene concentration following contact with the Ni—Nb—Taoxide mixtures, show significant ethane conversion to ethylene at 325°C. Table 37 lists CO and CO₂ production at 325° C.

Example 11 Ni—Nb—Ta Oxide Mixtures at Lower Calcination Temperature

Table 38 lists composition and mass of a Ni—Nb—Ta oxide library. Bulksamples of the oxide mixtures shown in Table 38 were prepared from 1.0 Mnickel (II) nitrate hexahydrate, 1.0 M niobium (V) oxalate and 1.0 Mtantalum oxalate aqueous stock solutions. A CAVRO automated liquiddispensing system was used to deliver aliquots of the aqueous stocksolutions into vessels. Each vessel contained about 1.9 ml of solution.Like Example 5, the metal precursors were separated from the aqueousphase by precipitation. Ammonium carbonate (1.62 M) was added to each ofthe solutions resulting in a solid precipitate. The mixture was allowedto settle at 25° C. for 3 hours. The solid precipitate was separatedfrom the aqueous phase by centrifuging at 4000 rpm for 10 minutes,followed by decanting the supernatant. The solid was dried in a vacuumoven at 60° C. for about an hour. The solid obtained was calcined in airunder the following temperature-time profile: The temperature of theoven was increased from room temperature to 300° C. at a rate of 2°C./min. The oven temperature was held at 300° C. for 8 hours. After 8hours at 300° C., the oxide mixtures were removed from the oven and wereallowed to cool to room temperature. The bulk samples were ground with aspatula to ensure consistent bulk density. The bulk samples wereevaluated for catalytic performance by contacting each sample withethane and oxygen in a parallel fixed bed reactor, described inExample 1. Reactant flow rate was 1.048 sccm per minute per reactorvessel (sample), and the reactant gas was comprised of 40.1% C₂H₆, 8.4%O₂ and 51.5% N₂. Tables 39 and 40 list ethane conversion and ethyleneselectivity at 300° C., respectively, for each of the Ni—Nb—Ta oxidemixtures listed in Table 38. The ethane dehydrogenation reaction wasalso carried out at 250° C. and Tables 41 and 42 list ethane conversionand ethylene selectivity at 250° C., respectively, for each of theNi—Nb—Ta oxide mixtures listed in Table 38.

To determine the effect of ethylene in the reactor feed on ethaneconversion and ethylene selectivity, selected mixed oxide samples listedin Table 38 were contacted in the parallel fixed bed reaction with a gasmixture comprised of 11.3% C₂H₄, 28.7% C₂H₆, 8.4% O₂ and 51.5% N₂.Reactant flow rate was maintained at 1.048 sccm per minute per reactorvessel (sample), and the fractions of C₂H₄, C₂H₆ and CO₂ in the reactorfeed were verified during screening by measuring the composition of gaseffluent from blank vessels in the parallel fixed bed reactor. Tables 43and 44, which list the selected samples as well as changes in ethane andethylene concentration following contact with the Ni—Nb—Ta oxidemixtures, show significant ethane conversion to ethylene at 300° C.Table 45 lists CO₂ production at 300° C. The test was repeated at 275°C. for the same selected samples.

Example 12 Ni—Nb, Ni—Co, Ni—Co—Nb, Ni—Nb—Al, Ni—Nb—Fe and OptimizedMo—V—Nb Oxide Mixtures: Ethylene in Reactor Feed

Table 46 lists composition and mass of Ni—Nb, Ni—Co, Ni—Co—Nb, Ni—Nb—Aland Ni—Nb—Fe oxide mixtures, as well as an optimized Mo—V—Nb oxidecatalyst. Bulk samples of each of these oxide mixtures were preparedusing aqueous methods described above. For the Ni—Nb—Al and Ni—Nb—Feoxide mixtures, methods similar to those of Example 5 were followedexcept that 1.0M aluminum nitrate and 1.0M ferric nitrate, were used,respectively. Bulk samples were evaluated for catalytic performance inODHE by contacting each sample with ethane, ethylene and oxygen in theparallel fixed bed reactor. The reactant gas was comprised of 11.6%C₂H₄, 28.5% C₂H₆, 8.4% O₂ and 51.5% N₂. Reactant flow rate wasmaintained at 1.048 sccm per minute per reactor vessel (sample), andfractions of C₂H₄ and C₂H₆ in the reactor feed were verified duringscreening by measuring the composition of gas effluent from blankvessels in the parallel fixed bed reactor. Table 46, which also listschanges in ethane and ethylene concentration following contact with theoxide mixtures, shows significant ethane conversion to ethylene for manyof the mixed oxides. Notable exceptions include two of the Mo—V—Nb oxidesamples.

Example 13 Ni—Nb Oxide Mixtures: Effect of Preparation on Performance

To gauge the influence of the bulk sample preparation method on catalystperformance, Ni—Nb oxide compositions were prepared using six differentreagents to precipitate the metal precursors. The reagents includeammonium hydroxide, tetraethylammonium hydroxide, potassium carbonate,sodium hydroxide, potassium hydroxide, and ammonium carbonate, asfollows: Ammonium hydroxide: 1.0 ml of ammonium hydroxide (28% ammoniain water) was added to a solution of nickel nitrate (1.0M, 1.29 ml),niobium oxalate (1.07M, 0.57 ml), and Cobalt (II) nitrate (0.07 ml,1.0M). The resulting mixture was centrifuged at 4000 rpm for 20 minutesand the solution was decanted. The solid was dried in a vacuum oven at60° C. and then calcined at a maximum temperature of 400° C. Ammoniumcarbonate: 2.9 ml of ammonium carbonate (1.57M) was added to a solutionof nickel nitrate (1.0M, 1.53 ml), niobium oxalate (0.52M, 0.87 ml), andTantalum oxalate (0.87 ml, 0.52M). Foam (CO₂) was formed accompaniedwith the formation of a solid. The resulting mixture was centrifuged at4000 rpm for 20 minutes and the solution was decanted. To the solid,about 5 ml of distilled water was added and then mixed. The resultingmixture was centrifuged at 4000 rpm for 20 minutes and the solution wasdecanted. The solid was dried in a vacuum oven at 60° C. and thencalcined at a maximum temperature of 400° C. Tetraethylammoniumhydroxide: 4.4 ml of tetraethylamminium hydroxide (1.14M) was added to asolution of nickel nitrate (1.0M, 2.60 ml) and niobium oxalate (0.70M,0.70 ml). The resulting mixture was centrifuged at 4000 rpm for 20minutes and the solution was decanted. To the solid, about 5 ml ofdistilled water was added and then mixed. The resulting mixture wascentrifuged at 4000 rpm for 20 minutes and the solution was decanted.The solid was dried in a vacuum oven at 60° C. and then calcined at amaximum temperature of 400° C. Potassium hydroxide: 0.6 ml of potassiumhydroxide (5.26M in water) was added to a solution of nickel nitrate(1.0M, 1.50 ml) and niobium oxalate (0.70M, 0.30 ml). The resultingmixture was centrifuged at 4000 rpm for 20 minutes and the solution wasdecanted. To the solid, about 5 ml of distilled water was added and thenmixed. The resulting mixture was centrifuged at 4000 rpm for 20 minutesand the solution was decanted. The solid was dried in a vacuum oven at60° C. and then calcined at a maximum temperature of 400° C. Sodiumhydroxide: 1.0 ml of sodium hydroxide (3.0M in water) was added to asolution of nickel nitrate (1.0M, 1.50 ml) and niobium oxalate (0.7M,0.30 ml). The resulting mixture was centrifuged at 4000 rpm for 20minutes and the solution was decanted. To the solid, about 5 ml ofdistilled water was added and then mixed. The resulting mixture wascentrifuged at 4000 rpm for 20 minutes and the solution was decanted.The solid was dried in a vacuum oven at 60° C. and then calcined at amaximum temperature of 400° C. Potassium carbonate: 1.5 ml of potassiumcarbonate (2.04M in water) was added to a solution of nickel nitrate(1.0M, 1.50 ml) and niobium oxalate (0.70M, 0.30 ml). The resultingmixture was centrifuged at 4000 rpm for 20 minutes and the solution wasdecanted. To the solid, about 5 ml of distilled water was added and thenmixed. The resulting mixture was centrifuged at 4000 rpm for 20 minutesand the solution was decanted. The solid was dried in a vacuum oven at60° C. and then calcined at a maximum temperature of 400° C. Table 47lists the compositions of the Ni—Nb oxide mixtures, which were evaluatedfor catalytic performance in ODHE by contacting each sample with ethaneand oxygen in a parallel fixed bed reactor. Reactant flow rate was 1.048sccm per minute per reactor vessel (sample), and the reactant gas wascomprised of 40.1% C₂H₆, 8.4% O₂ and 51.5% N₂. Tables 48 and 49 listethane conversion and ethylene selectivity at 300° C., respectively, foreach of the Ni—Nb oxide mixtures prepared using the six differentreagents.

Example 14 Ni—Ta Oxide Mixtures

Table 50 lists composition and mass of a Ni—Ta oxide library. The oxidemixtures were prepared from 1.0 M nickel (II) nitrate hexahydrate and1.0 M tantalum oxalate aqueous stock solutions. A CAVRO automated liquiddispensing system was used to deliver aliquots of the aqueous stocksolutions into vessels. Each vessel contained about 3.3 ml of solution.About 1.1 ml of a 1.14 M tetraethylammonium hydroxide solution was addedto each of the solutions resulting in a solid precipitate. The solidprecipitate was separated from the aqueous phase by centrifuging at 4000rpm for 20 minutes, followed by decanting the supernatant. The solid wasdried in a vacuum oven at 60° C. for about an hour, and then calcined inaccordance with the temperature-time profile described in Example 1. Thebulk samples were ground with a spatula to ensure consistent bulkdensity, and were evaluated for catalytic performance in ODHE bycontacting each sample with ethane and oxygen in a parallel fixed bedreactor. Reactant flow rate was 1.048 sccm per minute per reactor vessel(sample), and the reactant gas was comprised of 40.1% C₂H₆, 8.4% O₂ and51.5% N₂. Table 50 lists ethane conversion and ethylene selectivity at300° C. for each of the Ni—Ta oxide mixtures

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reading the above description. The scopeof the invention should therefore be determined not with reference tothe above description, but should instead be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. The disclosures of all articles andreferences, including patent applications and publications, areincorporated herein by reference for all purposes.

TABLE 1 Composition and mass of Ni—Co—Nb oxide mixtures Mole Fraction &Sample Mass, mg 1 2 3 4 5 6 7 1 Ni 0.89 Co 0.09 Nb 0.02 M 59.3 2 Ni 0.840.76 Co 0.10 0.22 Nb 0.06 0.02 M 35.5 59.5 3 Ni 0.78 0.69 0.62 Co 0.110.25 0.36 Nb 0.11 0.06 0.02 M 31.4 39.7 49.4 4 Ni 0.70 0.61 0.54 0.49 Co0.13 0.28 0.40 0.49 Nb 0.17 0.11 0.06 0.02 M 50.5 43.3 36.0 52.4 5 Ni0.59 0.51 0.44 0.40 0.36 Co 0.15 0.32 0.44 0.54 0.62 Nb 0.26 0.17 0.110.06 0.02 M 46.9 48.6 33.8 52.3 48.9 6 Ni 0.44 0.37 0.32 0.28 0.25 0.22Co 0.18 0.37 0.51 0.61 0.69 0.76 Nb 0.38 0.26 0.17 0.11 0.06 0.02 M 43.946.7 46.7 36.1 42.1 62.9 7 Ni 0.22 0.18 0.15 0.13 0.11 0.10 0.09 Co 0.220.44 0.59 0.70 0.78 0.84 0.89 Nb 0.56 0.38 0.26 0.17 0.11 0.06 0.02 M45.8 46.8 47.3 50.7 45.7 65.4 48.5

TABLE 2 Ethane conversion of Ni—Co—Nb oxide mixtures listed in Table 1Ethane Conversion, % 1 2 3 4 5 6 7 1 17.6 2 16.3 10.4 3 15.0 10.1 11.8 417.1 10.9 11.2 10.0 5 11.5 12.4 11.7 10.4 11.2 6 12.3 11.5 13.3 10.911.7 12.6 7 9.6 11.5 9.3 12.4 11.7 11.8 10.9

TABLE 3 Ethylene selectivity of Ni—Co—Nb oxide mixtures listed in Table1 Ethylene Selectivity, % 1 2 3 4 5 6 7 1 40.7 2 39.4 45.6 3 46.8 42.131.6 4 61.3 48.5 29.8 31.9 5 48.0 34.0 34.0 35.5 30.9 6 36.7 29.8 32.336.3 33.9 35.2 7 30.6 30.5 38.9 35.3 32.6 33.2 37.4

TABLE 4 Composition and mass of Ni-Co-Nb oxide mixtures 1 2 3 4 5 6 MoleFraction & Sample Mass, mg 1 Ni 0.73 0.71 0.69 0.67 0.65 0.63 Co 0.030.06 0.09 0.12 0.15 0.17 Nb 0.23 0.23 0.22 0.21 0.21 0.20 M 43.7 45.847.2 45.8 44.0 50.1 2 Ni 0.76 0.73 0.71 0.60 0.67 0.65 Co 0.03 0.07 0.100.13 0.15 0.18 Nb 0.21 0.20 0.19 0.19 0.18 0.18 M 44.3 44.0 48.5 42.943.6 47.1 3 Ni 0.79 0.76 0.73 0.71 0.69 0.67 Co 0.04 0.07 0.10 0.13 0.160.18 Nb 0.18 0.17 0.17 0.16 0.16 0.15 M 43.1 44.7 47.7 46.0 50.4 46.9 4Ni 0.81 0.79 0.76 0.73 0.71 0.69 Co 0.04 0.07 0.10 0.13 0.16 0.19 Nb0.14 0.14 0.14 0.13 0.13 0.13 M 42.8 41.4 44.6 42.8 44.5 43.1

TABLE 5 Ethane conversion of Ni-Co-Nb oxide mixtures listed in Table 4Ethane Conversion, % 1 2 3 4 5 6 1 22.8 16.4 16.8 13.6 13.3 13.5 2 21.416.2 19.5 15.9 14.6 14.9 3 22.7 15.7 16.9 15.4 15.5 15.0 4 17.3 14.015.6 14.5 13.9 15.0

TABLE 6 Ethylene selectivity of Ni-Co-Nb oxide mixtures listed in Table4 Ethylene Selectivity, % 1 2 3 4 5 6 1 62.2 70.1 56.4 52.7 45.8 44.0 266.3 69.8 66.1 61.5 50.1 46.3 3 64.8 71.7 61.8 60.8 55.7 52.3 4 63.869.6 59.8 57.0 51.3 48.0

TABLE 7 Composition and mass of Ni-Co-Nb oxide mixtures Mole Fraction &Sample Mass, mg 1 2 3 4 1 Ni 1.00 Co 0.00 Nb 0.00 M 45.6 2 Ni 0.85 0.840.83 0.82 Co 0.00 0.01 0.02 0.03 Nb 0.15 0.15 0.15 0.15 M 40.5 40.3 40.141.0 3 Ni 0.81 0.81 0.80 0.79 Co 0.00 0.01 0.02 0.03 Nb 0.19 0.18 0.180.18 M 39.2 43.8 41.6 41.6 4 Ni 0.79 0.78 0.77 0.77 Co 0.00 0.01 0.020.03 Nb 0.21 0.21 0.21 0.21 M 40.1 40.0 39.2 42.7 5 Ni 0.76 0.75 0.750.74 Co 0.00 0.01 0.02 0.03 Nb 0.24 0.24 0.24 0.24 M 39.3 40.9 40.9 39.96 Ni 0.73 0.73 0.72 0.72 Co 0.00 0.01 0.02 0.02 Nb 0.27 0.26 0.26 0.26 M42.7 40.3 41.6 40.3 7 Ni 0.71 0.70 0.70 0.69 Co 0.00 0.01 0.02 0.02 Nb0.29 0.29 0.29 0.28 M 42.0 41.7 43.6 46.3 8 Ni 0.69 Co 0.00 Nb 0.31 M42.8 9 Ni 0.67 Co 0.00 Nb 0.33 M 41.3 10 Ni 0.65 Co 0.00 Nb 0.35 M 41.411 Ni 0.63 Co 0.00 Nb 0.37 M 40.9 12 Ni 0.61 Co 0.00 Nb 0.39 M 40.0 13Ni 0.59 Co 0.00 Nb 0.41 M 41.8 14 Ni 0.58 Co 0.00 Nb 0.42 M 40.9 15 Ni0.56 Co 0.00 Nb 0.44 M 41.2 16 Ni 0.55 Co 0.00 Nb 0.45 M 41.8 17 Ni 0.54Co 0.00 Nb 0.46 M 40.0 18 Ni 0.52 Co 0.00 Nb 0.48 M 40.8 19 Ni 0.50 Co0.00 Nb 0.50 M 41.5

TABLE 8 Ethane conversion of Ni-Co-Nb oxide mixtures listed in Table 7Ethane Conversion, % 1 2 3 4 1 3.9 2 8.3 7.8 7.8 7.6 3 10.0 9.7 9.6 10.74 10.0 11.9 9.8 11.3 5 10.9 11.2 10.4 11.4 6 9.7 10.9 9.4 11.0 7 8.710.0 9.6 11.0 8 9.8 9 8.1 10 7.2 11 6.5 12 5.7 13 5.9 14 5.5 15 5.5 164.3 17 4.5 18 4.4 19 3.2

TABLE 9 Ethylene selectivity of Ni—Co—Nb oxide mixtures listed in Table7 Ethylene Selectivity, % 1 2 3 4 1 16.2 2 69.0 68.6 68.2 65.7 3 74.465.7 57.4 59.6 4 68.2 61.7 70.3 70.3 5 61.5 67.8 70.8 69.8 6 68.1 69.470.6 69.8 7 68.2 66.2 67.0 69.4 8 63.8 9 68.9 10 70.0 11 70.0 12 70.0 1364.5 14 70.4 15 72.5 16 72.2 17 73.1 18 68.0 19 74.7

TABLE 10 Compositions of Ni-Co-Nb oxide mixtures Mole Fraction & SampleMass, mg 1 2 3 4 5 6 7 8 9 10 11 1 Ni 1.00 Co 0.00 Nb 0.00 M 25.8 2 Ni0.90 0.90 Co 0.00 0.10 Nb 0.10 0.00 M 29.5 31.0 3 Ni 0.80 0.80 0.80 Co0.00 0.10 0.20 Nb 0.20 0.10 0.00 M 24.6 24.5 34.4 4 Ni 0.70 0.70 0.700.70 Co 0.00 0.10 0.20 0.30 Nb 0.30 0.20 0.10 0.00 M 26.4 37.0 30.3 29.95 Ni 0.60 0.60 0.60 0.60 0.60 Co 0.00 0.10 0.20 0.30 0.40 Nb 0.40 0.300.20 0.10 0.00 M 33.1 34.4 35.5 38.3 31.4 6 Ni 0.50 0.50 0.50 0.50 0.500.50 Co 0.00 0.10 0.20 0.30 0.40 0.50 Nb 0.50 0.40 0.30 0.20 0.10 0.00 M34.4 32.7 30.8 39.4 30.4 35.5 7 Ni 0.40 0.40 0.40 0.40 0.40 0.40 0.40 Co0.00 0.10 0.20 0.30 0.40 0.50 0.60 Nb 0.60 0.50 0.40 0.30 0.20 0.10 0.00M 34.6 37.5 30.1 30.4 34.3 32.3 30.9 8 Ni 0.30 0.30 0.30 0.30 0.30 0.300.30 0.30 Co 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 Nb 0.70 0.60 0.500.40 0.30 0.20 0.10 0.00 M 42.7 32.9 35.7 29.5 28.6 36.8 38.4 26.9 9 Ni0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 Co 0.00 0.10 0.20 0.30 0.400.50 0.60 0.70 0.80 Nb 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 M35.3 40.7 30.8 33.2 31.2 30.3 33.0 29.6 40.7 10 Ni 0.10 0.10 0.10 0.100.10 0.10 0.10 0.10 0.10 0.10 Co 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.700.80 0.90 Nb 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 M 34.433.2 53.4 32.7 28.8 25.0 22.8 35.6 31.0 25.6 11 Ni 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 Co 0.00 0.10 0.20 0.30 0.40 0.50 0.600.70 0.80 0.90 1.00 Nb 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.100.00 M 36.6 31.0 38.7 32.0 45.2 35.1 41.0 37.0 29.1 29.6 29.0

TABLE 11 Ethane conversion of Ni—Co—Nb oxide mixtures listed in Table 10Ethane Conversion, % 1 2 3 4 5 6 7 8 9 10 11 1 2.9 2 5.4 7.1 3 7.4 7.98.3 4 7.2 11.3 8.6 8.8 5 5.6 10.2 9.4 8.5 8.1 6 3.4 9.3 8.5 8.6 7.8 8.17 1.2 7.7 8.4 8.4 8.6 8.9 10.1 8 0.3 4.2 8.7 8.6 8.4 9.7 8.2 8.1 9 0.315.0 5.5 9.1 7.2 7.4 7.3 7.8 6.9 10 0.2 1.2 1.5 7.3 7.2 7.3 7.7 8.2 8.49.7 11 0.1 1.4 2.2 3.0 6.1 6.3 6.7 6.7 8.6 6.6 6.7

TABLE 12 Ethylene selectivity of Ni—Co—Nb oxide mixtures listed in Table10 Ethylene Selectivity, % 1 2 3 4 5 6 7 8 9 10 11 1 21.0 2 62.9 33.8 366.9 56.5 36.8 4 73.6 65.1 44.9 27.9 5 78.9 53.0 47.5 40.4 31.8 6 77.650.2 38.8 40.4 35.9 30.1 7 79.7 46.9 35.0 33.5 34.7 34.2 24.7 8 79.045.7 34.2 29.9 30.3 28.1 36.2 32.7 9 80.3 3.3 32.1 24.4 29.1 31.6 35.234.6 34.6 10 73.4 58.6 51.3 21.4 26.4 27.4 32.9 35.7 34.9 29.4 11 41.827.9 28.5 23.4 19.8 22.5 22.5 22.1 17.1 19.5 17.5

TABLE 13 Composition and mass of Ni-Co-Nb oxide mixtures 1 2 3 4 5 6 7 8Mole Fraction & Sample Mass, mg 1 Ni 1.00 Co 0.00 Nb 0.00 m 44.8 2 Ni0.92 0.96 Co 0.00 0.04 Nb 0.08 0.00 m 36.6 34.7 3 Ni 0.85 0.88 0.92 Co0.00 0.04 0.08 Nb 0.15 0.08 0.00 m 37.2 33.9 34.1 4 Ni 0.77 0.81 0.840.88 Co 0.00 0.04 0.08 0.12 Nb 0.23 0.16 0.08 0.00 m 40.8 35.8 35.8 42.25 Ni 0.70 0.73 0.76 0.80 0.83 Co 0.00 0.04 0.08 0.12 0.17 Nb 0.30 0.230.16 0.09 0.00 m 33.3 38.3 46.8 45.9 20.2 6 Ni 0.63 0.65 0.68 0.71 0.750.78 Co 0.00 0.04 0.08 0.12 0.17 0.22 Nb 0.37 0.31 0.24 0.17 0.09 0.00 m37.0 32.4 37.7 32.4 48.5 43.0 7 Ni 0.55 0.58 0.60 0.63 0.66 0.69 0.73 Co0.00 0.04 0.08 0.12 0.16 0.22 0.27 Nb 0.45 0.39 0.32 0.25 0.18 0.09 0.00m 48.9 38.3 30.2 32.4 32.5 40.6 36.9 8 Ni 0.48 0.50 0.52 0.55 0.57 0.600.63 0.67 Co 0.00 0.04 0.07 0.12 0.16 0.21 0.27 0.33 Nb 0.52 0.46 0.400.33 0.26 0.18 0.10 0.00 m 41.5 36.8 35.8 28.3 37.1 34.5 38.1 40.4

TABLE 14 Ethane conversion of Ni-Co-Nb oxide mixtures listed in Table 13Ethane Conversion, % 1 2 3 4 5 6 7 8 1 4.6 2 2.1 6.5 3 5.1 4.7 6.9 4 8.711.2 7.2 6.7 5 9.2 12.1 6.2 8.6 6.5 6 10.0 13.1 12.9 10.8 8.8 7.2 7 11.614.6 10.1 10.3 8.4 8.0 6.8 8 7.5 13.2 10.1 8.8 8.7 7.7 9.0 7.4

TABLE 15 Ethylene selectivity of Ni—Co—Nb oxide mixtures listed in Table13 Ethylene Selectivity, % 1 2 3 4 5 6 7 8 1 16.7 2 74.9 32.0 3 83.862.8 35.0 4 85.1 82.4 54.5 33.5 5 81.3 84.1 74.3 58.4 31.7 6 85.3 72.479.2 66.7 52.4 29.8 7 85.7 75.9 68.5 59.7 46.3 37.8 27.2 8 78.3 76.756.9 52.9 50.8 36.3 29.3 31.5

TABLE 16 Composition and mass of Ni—Nb—Ta—K oxide mixtures Mole Fraction& Sample Mass, mg 1 2 3 4 5 6 7 1 Ni 0.5837 Nb 0.3772 Ta 0.0391 K 0.0000M 38.7 2 Ni 0.5910 0.5916 Nb 0.3289 0.3292 Ta 0.0396 0.0792 K 0.04050.0000 M 35.4 38.4 3 Ni 0.5985 0.5991 0.5997 Nb 0.2793 0.2796 0.2799 Ta0.0401 0.0802 0.1204 K 0.0821 0.0411 0.0000 M 37.7 38.0 42.0 4 Ni 0.60620.6068 0.6074 0.6080 Nb 0.2285 0.2287 0.2290 0.2292 Ta 0.0406 0.08120.1220 0.1628 K 0.1247 0.0832 0.0417 0.0000 M 43.1 40.6 38.7 40.8 5 Ni0.6141 0.6147 0.6153 0.6160 0.6166 Nb 0.1764 0.1765 0.1767 0.1769 0.1771Ta 0.0411 0.0823 0.1235 0.1649 0.2063 K 0.1685 0.1265 0.0844 0.04220.0000 M 36.4 36.5 42.3 40.1 39.0 6 Ni 0.6222 0.6228 0.6235 0.62410.6247 0.6254 Nb 0.1228 0.1230 0.1231 0.1232 0.1233 0.1235 Ta 0.04160.0834 0.1252 0.1671 0.2091 0.2511 K 0.2134 0.1709 0.1283 0.0856 0.04290.0000 M 36.9 41.5 36.1 44.4 40.2 39.3 7 Ni 0.6305 0.6311 0.6318 0.63240.6331 0.6338 0.6345 Nb 0.0679 0.0680 0.0680 0.0681 0.0682 0.0683 0.0683Ta 0.0422 0.0845 0.1268 0.1693 0.2119 0.2545 0.2972 K 0.2595 0.21640.1733 0.1301 0.0869 0.0435 0.0000 M 39.7 40.4 38.8 51.4 45.6 42.9 43.9

TABLE 17 Ethane conversion of Ni—Nb—Ta—K oxide mixtures listed in Table16 Ethane Conversion, % 1 2 3 4 5 6 7 1 6.3 2 4.9 6.0 3 4.5 5.3 6.3 44.4 4.5 5.7 7.0 5 3.0 4.4 5.1 6.1 6.5 6 0.8 2.7 3.8 5.1 5.4 6.5 7 0.30.9 2.3 4.2 5.1 6.3 5.8

TABLE 18 Ethylene Selectivity of Ni—Nb—Ta—K oxide mixtures listed inTable 16 at 300° C. Ethylene Selectivity, % 1 2 3 4 5 6 7 1 80.6 2 62.384.8 3 45.5 68.4 85.2 4 34.4 49.4 73.1 84.6 5 16.3 35.4 55.4 76.9 85.9 61.3 17.4 37.2 54.6 80.9 85.2 7 0.0 1.0 8.7 39.1 59.1 78.3 86.9

TABLE 19 Composition and mass of Ni—Nb—Ta oxide mixtures uz,7/40 MoleFraction & Sample Mass, mg 1 2 3 4 5 6 7 1 Ni 0.95 Nb 0.03 Ta 0.02 M28.2 2 Ni 0.91 0.89 Nb 0.03 0.09 Ta 0.06 0.02 M 43.7 51.8 3 Ni 0.87 0.850.83 Nb 0.03 0.09 0.15 Ta 0.10 0.06 0.02 M 47.6 35.2 39.2 4 Ni 0.82 0.800.78 0.77 Nb 0.04 0.10 0.16 0.21 Ta 0.14 0.10 0.06 0.02 M 53.1 40.5 38.835.8 5 Ni 0.78 0.76 0.74 0.72 0.70 Nb 0.04 0.10 0.16 0.22 0.27 Ta 0.190.14 0.10 0.06 0.02 M 39.8 52.1 38.1 37.5 36.8 6 Ni 0.73 0.71 0.69 0.670.66 0.64 Nb 0.04 0.10 0.17 0.23 0.28 0.34 Ta 0.24 0.19 0.14 0.10 0.060.02 M 70.1 42.4 37.1 40.2 37.0 39.6 7 Ni 0.67 0.66 0.64 0.62 0.61 0.590.58 Nb 0.04 0.11 0.17 0.23 0.29 0.35 0.40 Ta 0.29 0.24 0.19 0.14 0.100.06 0.02 M 35.6 45.2 36.1 42.0 35.6 36.1 38.2

TABLE 20 Ethane conversion of Ni—Nb—Ta oxide mixtures listed in Table 19Ethane Conversion, % 1 2 3 4 5 6 7 1 2.0 2 4.1 3.8 3 3.8 6.1 7.9 4 4.12.6 5.3 6.1 5 2.8 3.8 4.5 6.9 6.4 6 5.4 3.2 6.6 3.3 7.1 6.4 7 3.9 3.95.2 3.7 5.3 7.0 6.1

TABLE 21 Ethylene selectivity of Ni—Nb—Ta oxide mixtures listed in Table19 Ethylene Selectivity, % 1 2 3 4 5 6 7 1 70.8 2 69.3 63.4 3 68.5 74.368.4 4 61.9 62.0 74.5 69.9 5 59.8 67.4 69.7 74.6 76.5 6 74.9 65.2 76.067.2 76.4 75.8 7 75.5 67.3 73.0 72.1 72.2 80.0 75.3

TABLE 22 Composition and mass of Ni—Nb—Ta oxide mixtures Mole Fraction &Sample Mass, mg 1 2 3 4 5 6 7 1 Ni 0.8621 Nb 0.0690 Ta 0.0690 M 39.3 2Ni 0.8128 0.8128 Nb 0.0725 0.1147 Ta 0.1147 0.0725 M 35.4 38.5 3 Ni0.7583 0.7583 0.7583 Nb 0.0763 0.1208 0.1654 Ta 0.1654 0.1208 0.0763 M43.7 43.2 39.7 4 Ni 0.6977 0.6977 0.6977 0.6977 Nb 0.0806 0.1276 0.17470.2217 Ta 0.2217 0.1747 0.1276 0.0806 M 50.8 38.1 38.2 36.9 5 Ni 0.62980.6298 0.6298 0.6298 0.6298 Nb 0.0854 0.1353 0.1851 0.2349 0.2848 Ta0.2848 0.2349 0.1851 0.1353 0.0854 M 48.9 43.6 47.5 48.3 41.8 6 Ni0.5533 0.5533 0.5533 0.5533 0.5533 0.5533 Nb 0.0909 0.1439 0.1969 0.24990.3029 0.3559 Ta 0.3559 0.3029 0.2499 0.1969 0.1439 0.0909 M 28.3 48.546.4 47.9 40.0 56.0 7 Ni 0.4664 0.4664 0.4664 0.4664 0.4664 0.46640.4664 Nb 0.0970 0.1536 0.2102 0.2668 0.3234 0.3800 0.4366 Ta 0.43660.3800 0.3234 0.2668 0.2102 0.1536 0.0970 M 51.8 34.1 49.2 35.7 42.547.5 62.7

TABLE 23 Ethane Conversion at 300° C. of Ni—Nb—Ta oxide mixtures listedin Table 22 Ethane Conversion, % 1 2 3 4 5 6 7 1 9.6 2 10.2 10.1 3 10.610.9 8.2 4 11.1 9.9 9.1 8.2 5 9.6 10.0 10.4 10.2 9.9 6 4.5 7.2 7.1 7.27.1 8.9 7 1.4 2.0 1.8 0.7 1.1 2.5 1.4

TABLE 24 Ethylene selectivity at 300° C. of Ni—Nb—Ta oxide mixtureslisted in Table 22 Ethylene Selectivity, % 1 2 3 4 5 6 7 1 80.4 2 80.182.8 3 84.0 84.5 84.5 4 81.8 84.0 82.7 84.3 5 86.8 84.6 86.3 86.9 87.0 684.2 88.1 89.1 87.2 87.6 90.1 7 82.5 84.7 86.6 79.4 86.6 87.8 80.5

TABLE 25 Ethane Conversion at 325° C. of Ni—Nb—Ta oxide mixtures listedin Table 22 Ethane Conversion, % 1 2 3 4 5 6 7 1 14.6 2 15.9 14.5 3 15.216.0 12.6 4 15.9 14.5 13.6 12.7 5 14.3 15.5 15.4 15.2 14.8 6 8.2 11.811.4 11.6 11.8 13.9 7 2.5 3.9 3.4 1.4 1.9 5.0 2.7

TABLE 26 Ethylene selectivity at 325° C. of Ni—Nb—Ta oxide mixtureslisted in Table 22 Ethylene Selectivity, % 1 2 3 4 5 6 7 1 84.2 2 81.784.5 3 83.9 84.9 84.3 4 82.5 86.0 83.4 84.6 5 87.8 86.8 85.9 86.8 87.8 683.8 87.5 88.2 87.8 86.1 88.9 7 81.5 84.2 86.0 77.2 85.2 86.4 78.5

TABLE 27 Difference in ethylene concentration between reactor effluentand feed for Ni—Nb—Ta oxide mixtures listed in Table 22 (C₂H₆/C₂H₄ Feed)Δ C₂H₄, % 1 2 3 4 5 6 7 1 7.0 2 7.2 6.2 3 5.1 6.4 5.0 4 6.8 6.6 4.7 5.35 7.3 7.3 5.9 7.1 7.1 6 4.0 5.6 5.4 5.7 5.3 6.1 7 1.2 2.0 1.4 −0.4 0.82.2 1.0

TABLE 28 Difference in ethane concentration between reactor effluent andfeed for Ni—Nb—Ta oxide mixtures listed in Table 22 (C₂H₆/C₂H₄ Feed) ΔC₂H₄, % 1 2 3 4 5 6 7 1 −9.3 2 −10.5 −8.3 3 −8.1 −9.3 −7.4 4 −9.9 −8.6−7.2 −7.5 5 −8.9 −9.3 −8.4 −9.4 −8.8 6 −5.3 −7.1 −6.8 −7.1 −7.3 −7.9 7−1.3 −2.3 −1.7 0.4 −0.8 −2.9 −1.3

TABLE 29 Difference in carbon monoxide and carbon dioxide betweenreactor effluent and feed for Ni—Nb—Ta oxide mixtures listed in Table 22(C₂H₆/C₂H₄ Feed) Δ CO & CO₂, % 1 2 3 4 5 6 7 1 2.2 2 3.3 2.2 3 2.9 2.92.4 4 3.1 1.9 2.5 2.2 5 1.7 1.9 2.5 2.3 1.8 6 1.3 1.5 1.4 1.4 1.9 1.8 70.1 0.3 0.3 0.0 0.0 0.7 0.3

TABLE 30 Composition and mass of Ni—Nb—Ta oxide mixtures Mole Fraction &Sample Mass, mg 1 2 3 4 5 6 1 Ni 0.7194 0.7196 0.7197 0.7199 0.72010.7202 Nb 0.2324 0.1937 0.1550 0.1163 0.0775 0.0388 Ta 0.0481 0.08670.1252 0.1638 0.2024 0.2410 M 44.6 42.8 38.4 37.1 48.8 41.5 2 Ni 0 .69590.6960 0.6962 0.6964 0.6965 0.6967 Nb 0.2519 0.2100 0.1680 0.1261 0.08410.0420 Ta 0.0522 0.0940 0.1358 0.1776 0.2194 0.2613 M 40.1 40.5 39.036.8 44.4 49.9 3 Ni 0.6680 0.6682 0.6683 0.6685 0.6687 0.6689 Nb 0.27500.2293 0.1835 0.1376 0.0918 0.0459 Ta 0.0570 0.1026 0.1482 0.1939 0.23950.2852 M 35.6 37.0 40.7 41.0 44.2 51.9 4 Ni 0.6345 0.6346 0.6348 0.63500.6352 0.6354 Nb 0.3028 0.2524 0.2020 0.1515 0.1011 0.0505 Ta 0.06270.1129 0.1632 0.2135 0.2638 0.3141 M 37.9 38.6 37.0 34.8 35.9 36.4 5 Ni0.5934 0.5936 0.5938 0.5940 0.5942 0.5944 Nb 0.3368 0.2808 0.2247 0.16860.1124 0.0562 Ta 0.0698 0.1256 0.1815 0.2374 0.2934 0.3494 M 36.5 36.036.6 41.5 35.6 35.4 6 Ni 0.5420 0.5422 0.5424 0.5426 0.5428 0.5430 Nb0.3794 0.3163 0.2531 0.1899 0.1267 0.0633 Ta 0.0786 0.1414 0.2045 0.26750.3306 0.3937 M 36.8 38.1 39.9 39.2 33.9 35.8

TABLE 31 Ethane Conversion at 300° C. of Ni—Nb—Ta oxide mixtures listedin Table 30 Ethane Conversion, % 1 2 3 4 5 6 Ethane Conversion, % 1 5.83.8 3.3 4.3 5.2 4.1 2 3.8 4.4 4.5 3.8 3.9 3.7 3 7.5 9.6 10.3 7.6 6.1 6.94 7.8 7.5 8.4 9.1 9.8 9.9 5 8.5 8.1 8.2 8.9 9.2 10.2 6 9.6 9.1 10.3 10.410.7 11.6

TABLE 32 Ethylene selectivity at 300° C. of Ni—Nb—Ta oxide mixtureslisted in Table 30 Ethylene Selectivity, % 1 2 3 4 5 6 EthyleneSelectivity, % 1 87.2 88.0 88.2 89.4 89.3 89.6 2 86.4 87.1 89.2 90.487.3 87.7 3 85.1 84.4 81.8 85.4 90.5 89.0 4 82.8 84.0 85.2 85.4 83.583.8 5 80.2 83.1 84.6 85.0 85.5 85.9 6 77.5 78.1 81.5 84.1 83.3 85.3

TABLE 33 Ethane conversion at 325° C. of Ni—Nb—Ta oxide mixtures listedin Table 30 Ethane Conversion, % 1 2 3 4 5 6 Ethane Conversion, % 1 8.76.7 5.7 7.3 8.8 6.8 2 6.7 7.3 7.2 6.2 6.5 6.3 3 11.7 13.3 13.9 11.5 9.611.1 4 12.2 11.7 12.2 12.8 14.0 14.4 5 12.8 12.0 13.0 13.7 14.0 15.4 614.1 14.0 15.9 15.6 16.5 16.9

TABLE 34 Ethylene selectivity at 325° C. of Ni—Nb—Ta oxide mixtureslisted in Table 30 Ethylene Selectivity 1 2 3 4 5 6 Ethylene Selectivity1 85.7 85.6 85.9 86.8 87.5 88.6 2 84.4 85.1 86.3 88.1 85.6 85.6 3 84.383.7 84.9 84.8 89.4 88.0 4 84.0 83.8 85.4 84.0 85.2 84.5 5 81.3 83.984.1 84.5 84.5 85.9 6 82.3 81.4 83.5 84.2 85.0 85.8

TABLE 35 Difference in ethylene concentration between reactor effluentand feed for Ni—Nb—Ta oxide mixtures listed in Table 30 (C₂H₆/C₂H₄ Feed)Δ C₂H₄, % 1 2 3 4 5 6 Δ C₂H₄, % 1 2.3 1.1 0.6 0.4 2.3 1.8 2 1.2 1.2 0.51.2 1.5 0.9 3 3.1 4.6 5.6 4.2 3.7 4.2 4 4.6 4.1 4.4 4.2 5.5 5.4 5 3.74.2 4.6 4.6 4.0 6.1 6 6.0 5.3 5.9 5.0 6.8 7.0

TABLE 36 Difference in ethane concentration between reactor effluent andfeed for Ni—Nb—Ta oxide mixtures listed in Table 30 (C₂H₆/C₂H₄ Feed) ΔC₂H₆, % 1 2 3 4 5 6 Δ C₂H₆, % 1 −3.8 −2.8 −2.1 −2.4 −4.2 −3.1 2 −2.9−3.0 −2.3 −2.7 −2.9 −2.5 3 −5.6 −7.0 −8.3 −6.2 −5.1 −5.9 4 −6.6 −6.2−6.8 −6.6 −7.7 −7.8 5 −6.5 −6.5 −6.8 −7.0 −6.8 −9.0 6 −8.3 −8.0 −8.7−8.1 −9.8 −9.9

TABLE 37 Difference in carbon monoxide and carbon dioxide betweenreactor effluent and feed for Ni—Nb—Ta oxide mixtures listed in Table 30(C₂H₆/C₂H₄ Feed) Δ CO & CO₂, % 1 2 3 4 5 6 1 1.5 1.7 1.5 1.9 1.9 1.4 21.7 1.8 1.8 1.4 1.4 1.6 3 2.5 2.5 2.6 2.1 1.4 1.7 4 1.9 2.1 2.4 2.4 2.22.5 5 2.8 2.3 2.3 2.4 2.8 2.9 6 2.3 2.6 2.9 3.1 3.0 2.9

TABLE 38 Composition and mass of Ni—Nb—Ta oxide mixtures calcined at300° C. Mole Fraction & Sample Mass, mg 1 2 3 4 5 6 1 Ni 1.000 Nb 0.000Ta 0.000 M 56.1 2 Ni 0.883 0.890 Nb 0.000 0.110 Ta 0.117 0.000 M 46.058.0 3 Ni 0.782 0.787 0.793 Nb 0.000 0.103 0.208 Ta 0.218 0.110 0.000 M45.4 57.2 47.7 4 Ni 0.693 0.698 0.702 0.706 Nb 0.000 0.097 0.195 0.294Ta 0.307 0.206 0.104 0.000 M 49.9 46.5 45.2 50.0 5 Ni 0.615 0.618 0.6220.626 0.629 Nb 0.000 0.091 0.183 0.276 0.371 Ta 0.385 0.291 0.195 0.0980.000 M 51.5 52.0 47.5 55.3 54.2 6 Ni 0.545 0.548 0.551 0.554 0.5570.560 Nb 0.000 0.086 0.173 0.261 0.350 0.440 Ta 0.455 0.366 0.276 0.1850.093 0.000 M 54.5 54.6 57.2 59.6 54.3 50.8

TABLE 39 Ethane Conversion at 300° C. of Ni—Nb—Ta oxide mixtures listedin Table 38 Ethane Conversion, % 1 2 3 4 5 6 1 10.5 2 12.0 17.7 3 18.919.2 15.4 4 18.6 18.4 20.0 — 5 18.6 19.9 20.0 20.5 19.0 6 15.2 18.9 16.919.0 18.1 16.9

TABLE 40 Ethylene selectivity at 300° C. of Ni—Nb—Ta oxide mixtureslisted in Table 38 Ethylene Selectivity, % 1 2 3 4 5 6 EthyleneSelectivity, % 1 53.6 2 54.9 81.6 3 83.3 83.9 77.4 4 83.3 84.4 85.2 — 584.4 85.1 86.1 86.2 84.7 6 83.9 84.6 84.2 86.0 84.8 80.9

TABLE 41 Ethane Conversion at 250° C. of Ni—Nb—Ta oxide mixtures listedin Table 38 Ethane Conversion, % 1 2 3 4 5 6 1 5.4 2 5.7 9.7 3 9.8 11.05.9 4 9.8 4.5 5.5 — 5 4.6 4.5 4.6 5.1 4.5 6 2.9 4.1 3.3 4.5 4.2 4.0

TABLE 42 Ethylene selectivity at 250° C. of Ni—Nb—Ta oxide mixtureslisted in Table 38 Ethylene Selectivity, % 1 2 3 4 5 6 1 27.6 2 32.876.2 3 79.9 79.9 68.6 4 78.6 77.4 81.6 — 5 77.5 80.4 84.4 85.0 76.4 681.7 79.3 81.1 85.5 78.3 69.9

TABLE 43 Difference in ethylene concentration between reactor effluentand feed for Ni—Nb—Ta oxide mixtures listed in Table 38 (C₂H₆/C₂H₄ Feed)Δ C₂H₄, % 1 2 3 4 5 6 1 2 3 4 7.3 6.3 5 6.5 7.4 6.1 6.4 7.2 6 5.4 7.15.2 6.0 7.0 5.6

TABLE 44 Difference in ethane concentration between reactor effluent andfeed for Ni—Nb—Ta oxide mixtures listed in Table 38 (C₂H₆/C₂H₄ Feed) ΔC₂H₆, % 1 2 3 4 5 6 1 2 3 4 −10.3 −9.8 5 −9.7 −10.8 −9.3 −9.7 −10.3 6−7.9 −10.2 −8.2 −9.2 −10.0 −8.9

TABLE 45 Difference in carbon monoxide and carbon dioxide betweenreactor effluent and feed for Ni—Nb—Ta oxide mixtures listed in Table 38(C₂H₆/C₂H₄ Feed) Δ CO & CO₂, % 1 2 3 4 5 6 1 2 3 4 3.0 3.6 5 3.2 3.5 3.23.4 3.2 6 2.5 3.2 3.0 3.2 3.1 3.4

TABLE 46 Composition and mass of Ni-13 Nb, Ni—Co, Ni—Co—Nb, Ni—Nb—Al,Ni—Nb—F3, and Mo—V—Nb oxide mixtures; difference in ethane and ethyleneconcentration between reactor effluent and feed; carbon monoxide andcarbon dioxide production. Sample Δ C₂H₄ Δ C₂H₆ Δ CO & m, Mole FractionID % % CO₂, % mg Ni Co Nb Al Fe MoVNb −1.1 −0.4 1.8 40.8 Blank 0.2 −0.30.4 0.0 21187.12 3.4 −6.0 3.0 39.4 0.60 0.00 0.6 0.05 0.00 21187.31 4.0−72 3.5 41.5 0.61 0.00 0.36 0.00 0.02 21187.32 3.3 −6.8 3.8 38.9 0.600.00 0.36 0.00 0.05 21187.33 2.0 −5.6 3.9 40.7 0.58 0.00 0.35 0.00 0.0710717.31 4.7 −6.8 2.4 41.2 0.85 0.00 0.15 0.00 0.00 10717.41 6.7 −9.93.5 39.9 0.77 0.00 0.23 0.00 0.00 10717.42 7.2 −10.3 3.4 40.2 0.81 0.040.16 0.00 0.00 10717.52 7.3 −10.5 3.5 41.8 0.73 0.04 0.23 0.00 0.0010717.53 2.3 −5.1 3.0 40.6 0.76 0.08 0.16 0.00 0.00 10717.62 0.7 −5.65.2 40.1 0.65 0.04 0.31 0.00 0.00 10717.63 4.7 −8.2 3.8 41.6 0.68 0.080.24 0.00 0.00 10717.71 5.7 −8.4 3.0 41.0 0.55 0.00 0.45 0.00 0.00 MoVNb0.00 −1.4 1.8 40.9 10717.72 6.5 −10.5 4.3 40.5 0.58 0.04 0.39 0.00 0.0010717.73 −5.1 0.6 4.8 41.3 0.60 0.08 0.32 0.00 0.00 10615.41 2.7 −6.13.8 40.3 0.70 0.00 0.30 0.00 0.00 10615.42 3.2 −6.7 3.8 40.3 0.70 0.100.20 0.00 0.00 10615.51 1.6 −3.8 2.5 39.5 0.60 0.00 0.40 0.00 0.0010615.52 1.6 −5.7 4.3 38.3 0.60 0.10 0.30 0.00 0.00 21122.21 4.6 −8.64.3 39.4 0.84 0.01 0.15 0.00 0.00 21122.22 2.3 −6.6 4.6 32.2 0.81 0.010.18 0.00 0.00 21122.23 4.0 −7.7 4.0 39.6 0.78 0.01 0.21 0.00 0.00 Blank−0.3 0.2 0.4 0.0 21122.24 4.8 −9.4 4.9 40.3 0.75 0.01 0.24 0.00 0.0021122.25 3.5 −7.4 4.2 40.1 0.73 0.01 0.26 0.00 0.00 21122.13 4.7 −9.24.7 39.9 0.79 0.00 0.21 0.00 0.00 21122.14 4.5 −8.4 4.2 38.8 0.76 0.000.24 0.00 0.00 21122.31 4.6 −8.2 3.9 38.9 0.83 0.02 0.15 0.00 0.0021122.33 5.6 −9.1 3.8 39.3 0.77 0.02 0.21 0.00 0.00 21122.42 4.8 −8.43.0 39.1 0.79 0.03 0.18 0.00 0.00 21122.43 5.6 −10.4 5.1 42.2 0.77 0.030.21 0.00 0.00 21123.1 6.2 −10.6 4.7 40.6 0.69 0.00 0.31 0.00 0.0021123.2 5.6 −9.9 4.6 40.3 0.67 0.00 0.33 0.00 0.00 21123.2 5.6 −9.1 3.842.0 0.65 0.00 0.35 0.00 0.00 21123.5 5.2 −8.1 3.1 40.3 0.61 0.00 0.390.00 0.00 21123.7 5.6 −8.2 2.9 40.3 0.59 0.00 0.41 0.00 0.00 MoVNb 2.1−3.4 1.6 41.9 10652.31 8.7 −12.6 4.2 41.7 0.80 0.00 0.20 0.00 0.0010652.41 6.4 −10.6 4.5 38.5 0.70 0.00 0.30 0.00 0.00 10652.61 3.7 −5.92.5 39.7 0.50 0.00 0.50 0.00 0.00 10793.1 8.3 −10.5 2.5 39.2 0.86 0.000.14 0.00 0.00 10793.3 8.1 −10.4 2.6 39.1 0.81 0.00 0.19 0.00 0.0010793.5 5.5 −6.9 1.7 37.9 0.75 0.00 0.25 0.00 0.00

TABLE 47 Composition of Ni—Nb oxide mixtures Mole Fraction & SampleMass, mg 1 2 3 4 1 Ni 0.8772 0.7692 0.6736 0.5882 Nb 0.1228 0.23080.3264 0.4118 M 17.1 36.9 39.3 36.5 2 Ni 0.8772 0.7692 0.6736 0.5882 Nb0.1228 0.2308 0.3264 0.4118 M 37.4 37.2 40.3 39.0 3 Ni 0.8772 0.76920.6736 0.5882 Nb 0.1228 0.2308 0.3264 0.4118 M 42.1 42.4 48.3 41.0 4 Ni0.8772 0.7692 0.6736 0.5882 Nb 0.1228 0.2308 0.3264 0.4118 M 50.3 39.338.0 39.7 5 Ni 0.8772 0.7692 0.6736 0.5882 Nb 0.1228 0.2308 0.32640.4118 M 37.8 39.1 48.9 50.4 6 Ni 0.8772 0.7692 0.6736 0.5882 Nb 0.12280.2308 0.3264 0.4118 M 36.6 38.3 39.0 40.4

TABLE 48 Ethane Conversion of Ni—Nb oxide mixtures listed in Table 47Precipitation Ethane Conversion % Method 1 2 3 4 1 NH₄OH 0.9 8.9 7.3 6.82 NEt₄OH 8.9 6.2 8.6 11.4 3 K₂CO₃ 0.0 0.0 0.0 0.1 4 NaOH 0.3 2.4 3.6 4.25 KOH 0.5 0.2 0.0 0.1 6 (NH₄)₂CO₃ 10.7 11.2 11.4 10.5

TABLE 49 Ethylene Selectivity of Ni—Nb oxide mixtures listed in Table 47Precipitation Ethylene Selectivity, % Method 1 2 3 4 1 NH₄OH 78.3 78.874.5 72.3 2 NEt₄OH 82.4 88.0 88.1 83.1 3 K₂CO₃ 0.0 50.1 27.3 0.0 4 NaOH3.4 15.0 21.8 21.8 5 KOH 3.5 4.5 0.0 0.0 6 (NH₄)₂CO₃ 80.7 82.6 87.1 83.6

TABLE 50 Composition and mass of Ni—Ta oxide mixtures; ethane conversionand ethylene selectivity Mole Fraction & Ethane Conversion EthyleneSelectivity Sample Mass, mg % % Ni 0.50 8.1 87.8 Ta 0.50 m 81.8 Ni 0.558.0 89.5 Ta 0.45 m 59.2 Ni 0.61 8.6 86.6 Ta 0.39 m 55.8 Ni 0.67 7.9 85.8Ta 0.33 m 41.5 Ni 0.74 8.8 86.9 Ta 0.26 m 41.4 Ni 0.81 9.5 87.4 Ta 0.19m 43.3

1. A process for the oxidative dehydrogenation of an alkane having from2 to 4 carbon atoms to an alkene, comprising contacting said alkane inthe presence of oxygen to a compound that includes at least about 50%nickel oxide by weight at a temperature of about 400° C. or less,wherein said contacting is conducted in the presence of said alkene; andobtaining a selectivity in said dehydrogenation of greater than 70% anda conversion of greater than 10%.
 2. The process of claim 1 wherein saidselectivity is greater than 80%.
 3. The process of claim 2 wherein saidselectivity is greater than 85%.
 4. The method of claim 1 wherein saidconversion is greater than 15%.
 5. A process for the oxidativedehydrogenation of an alkane having from 2 to 4 carbon atoms to analkene, comprising providing a reactor and a reactor feed comprising agas mixture, wherein said gas mixture comprises said alkane, said alkeneand oxygen; contacting said gas mixture to a catalyst that includes atleast about 50% nickel oxide in said reactor, wherein said contacting isperformed at a temperature of about 400° C. or less; and obtaining aselectivity greater than 70% and a conversion greater than 10%.
 6. Theprocess of claim 5 wherein said selectivity is greater than 80%.
 7. Theprocess of claim 6 wherein said selectivity is greater than 85%.
 8. Theprocess of claim 5 wherein said conversion is greater than 15%.
 9. Amethod for the oxidative dehydrogenation of ethane to ethylene,optionally with ethylene as a co-feed with said ethane, comprisingcontacting ethane in the presence of oxygen to a catalyst that includesat least about 50% nickel oxide by weight with either niobium oxide ortantalum oxide.
 10. The method according to claim 9, wherein thecontacting step is carried out at a temperature of about 400° C. orless.
 11. The method according to claim 1, wherein said alkane is ethaneand said alkene is ethylene.
 12. The method according to claim 1,wherein said catalyst further comprises niobium oxide, tantalum oxide ora combination thereof.
 13. The method according to claim 1, wherein saidtemperature is between about 250° C. and 400° C.
 14. The methodaccording to claim 5, wherein said alkane is ethane and said alkene isethylene.
 15. The method according to claim 5, wherein said catalystfurther comprises niobium oxide, tantalum oxide or a combinationthereof.
 16. The method according to claim 5, wherein said temperatureis between about 250° C. and 400° C.
 17. The method according to claim9, wherein said catalyst comprises niobium oxide and tantalum oxide. 18.The method according to claim 14, wherein said temperature is betweenabout 250° C. and 400° C.